The present application claims priority under 35 U.S.C xc2xa7119 based upon Swiss Patent Application No. 2001 0926/01 filed May 16, 2001.
The invention concerns a pressure sensor.
With the mounting of semiconductor chips, the semiconductor chips are bonded to the substrate with an epoxy adhesive. In doing so, it is necessary that a precisely defined amount of adhesive is applied to the substrate. Application of the adhesive takes place for example with a dispensing nozzle as is described in the European patent application EP 928637. A pressure pulse is applied to the adhesive in the dispensing nozzle. Pressure sensors are used to control the pressure pulse.
A pressure sensor suitable for such measurements is offered by Honeywell under the designation 22 PC series. Basically, the pressure sensor comprises a membrane clamped in a body the deflection of which is measured in comparison with the body. For this purpose, piezoresistors are integrated into the surface of the membrane. In a first embodiment, there are pressure sensors for measuring a relative pressure with which the pressure to be measured is applied to the front of the membrane while the rear of the membrane is in contact with the ambient air. In a second embodiment, there are also pressure sensors for measuring an absolute pressure with which the rear of the membrane is sealed air-tight against the ambient air. The disadvantage with these sensors is that both the zero line as well as the characteristic curve change as time goes on which demands re-calibration at specific time intervals.
The object of the invention is to propose a pressure sensor which can be calibrated in a simple way.
The invention is based on the knowledge that force sensors from Honeywell of the same family as the above-mentioned pressure sensors are available on the market under the series FSG and FSL. With these force sensors, the force to be measured is transmitted to the membrane via a piston. On the one hand, such a force sensor is now expanded with a force transmitter or a positioner and, on the other hand, is modified so that the pressure to be measured can be applied to the side of the membrane facing away from the piston. In normal operation of the pressure sensor, the force transmitter or positioner have no function. The force transmitter or positioner serve only for the calibration of the pressure sensor. For the calibration of the pressure sensor, the membrane is deformed under defined conditions and then the output signal of the pressure sensor is ascertained. The deformation of the membrane is achieved either under the influence of a predetermined force exerted by the force transmitter on the piston, or by means of shifting the piston into a precisely defined position.
The pressure sensor can be used for measuring an overpressure as well as an underpressure or vacuum.
In the following, embodiments of the invention are explained in more detail based on the drawing.